A former CIA spy made an appearance, a quiet appearance, in U.S. District Court this week. He is charged with retaining classified materials. And this comes as the CIA is trying to understand why, beginning in 2010, its informants in China began vanishing, jailed and executed. Here's NPR's Greg Myre with more.

GREG MYRE, BYLINE: The case against Jerry Chun Shing Lee sounds like it belongs to an earlier age of espionage. A dual citizen of the U.S. and China, Lee, 53, was a CIA spy for more than a decade. After leaving the agency, he settled in Hong Kong. Lee visited Hawaii and Virginia in 2012. During his trip, the FBI sneaked into his hotel room and says it found two small books with handwritten names and phone numbers of CIA employees and informants. This was classified information he shouldn't have had, yet Lee wasn't arrested.

CHRIS JOHNSON: Perhaps they were trying to build a more significant case against him. It's hard to know.

MYRE: Chris Johnson is a former CIA China analyst who's now at the Center for Strategic and International Studies.

JOHNSON: But it does speak, I think, to the complexities of the game, if you will, these days that there was this seemingly unexplainable interregnum and then they finally went ahead and arrested him this time.

MYRE: It's important to note that Lee is accused of retaining classified information. He has not been charged with passing it on to the Chinese government. The New York Times and other media outlets report he's suspected of doing so. The CIA and the FBI aren't commenting. Lee's case is unusual when it comes to China. Chinese espionage is more often cyber snooping.

MARTIN LIBICKI: Based on what I see in cyberspace, they are dedicated, they are vigorous, they are persistent.

MYRE: Martin Libicki is a professor at the U.S. Naval Academy and author of "Cyberspace In Peace And War."

LIBICKI: I think one former head of the FBI compared the Chinese to a bunch of drunken burglars going through your house.

MYRE: The U.S. begin naming and shaming Chinese hackers several years ago, and the countries then reached a 2015 agreement pledging not to steal each other's intellectual property.

LAURA GALANTE: The Chinese military particularly had been hacking lots of R and D, from the energy sector, particularly in solar, all the way through to military application, fighter jets on down.

MYRE: Laura Galante used to monitor cyberthreats for the Defense Department and is now at the Atlantic Council. To the surprise of many, she says, the agreement is mostly working.

GALANTE: We did see a far diminished amount of hacking of intellectual property.

MYRE: Still, the spy games continue on multiple fronts. CIA Director Mike Pompeo says the Chinese target U.S. universities, the medical industry and corporations. Of course, the U.S. is spying on China and others. Here's how he describes U.S. efforts globally.

MIKE POMPEO: We ask our officers to risk their lives, to seal secrets, to protect America. It's our fundamental mission. We will never shy away from it, and we do so aggressively and without any apology.

MYRE: The U.S. and China are deeply entwined. Students, academics and businesspeople flow freely in both directions, which creates opportunities to spy and be spied upon. Here's Chris Johnson again, the former CIA analyst.

JOHNSON: The tricky bit is really more in the broader context of the U.S.-China relationship where we have this deepening economic interdependence. We cannot wall ourselves off from the Chinese economy, and they cannot wall themselves off from our economy.

MYRE: As a dual citizen, Jerry Lee could move back and forth freely during his time at the CIA. In turn, Chinese intelligence has a reputation for recruiting Americans who are ethnic Chinese. If convicted of retaining classified information, Lee faces up to 10 years in prison. Greg Myre, NPR News, Washington. Transcript provided by NPR, Copyright NPR.